1. Field of the Invention
The present invention generally relates to an air conditioning system for buildings and more particularly, to an air conditioning system of a type in which thermal energy is conducted through gravity type heat pipes.
2. Description of the Related Art
Generally, in an air conditioning system for a building, water has been used as a thermal medium for facilitating thermal conveyance between the thermal source equipment and the individual air conditioners. Such use of water, however, presented a problem of water leakage from an air conditioner. Recently, therefore, for air conditioning system for buildings, introduction of a volatile substance, such as freon, as a thermal medium to be passed directly between the thermal source equipment and the respective heat exchangers of the air conditioners, is being considered to reduce the problem of liquid leakage by virtue of the volatility of the substance.
The inventors have provided such a type of air conditioning system which utilizes gravity type heat pipes (refer to U.S. patent application No. 113,761). This air conditioning system includes a first thermal storage tank as a cold thermal reservoir which is installed at a high place, such as the roof, in an air-conditioned building; a second thermal storage tank as a hot thermal reservoir which is installed at a low place, such as the basement, in the same building; a plurality of air conditioners each of which is installed in a room to be air-conditioned or at a place close to it such as at floor level, between the first thermal storage tank as a cold thermal reservoir and the second thermal storage tank as a hot thermal source; and gravity type heat pipes which connect the air-conditioner with the first heat storage tank and with the second heat storage thank. The gravity type heat pipes are essentially designed to allow thermal medium to circulate therethrough under a natural pressure generated by a phase change of the thermal medium.
In the air conditioning system as described above the flow of the circulating thermal medium is adjusted to control the warming and cooling conditions in accordance with the required heat load in the respective air-conditioned rooms. It is to be noted, however, there are some problems associated with controlling the flow of the thermal medium. For example, when the air conditioners are installed on the different floors, the water head of the thermal medium in liquid phase is different between the respective air conditioners, resulting in that the degree of heat exchange is not equal in the respective air conditioners. More specifically, since the air conditioner arranged at a lower floor has a higher water head, flow control by a throttle valve or the like is very difficult. When the throttle valve is overly throttled, the thermal medium is not sufficiently supplied to the air conditioner. On the other hand, if the heat pipe vapor through which vapor passes at this air conditioner is filled by liquid thermal medium, a smooth flow of the vaporized thermal medium is hampered so that the heat exchange at the air conditioner can not be effected efficiently, resulting in poor cooling by the air conditioner. In addition, in the state in which a higher water head is caused, the temperature of the thermal medium in a vapor phase is relatively high so that sufficient cooling can not be obtained.
Moreover, when the heat loads at the different air-conditoned rooms are different from each other, the warming and cooling operations at these rooms must be separately adjusted in accordance with the specific heat loads and accordingly, when, for instance, the air conditioning system is operated in the cooling mode, in an air conditioner being subject to a larger heat load, the amount of exchanged heat and accordingly the amount of vapor of the thermal medium become larger so that the resistance in the heat pipe through which the vapor passes becomes larger, that is, since the line or the air conditioners requiring a larger quantity of thermal medium offer larger resistance, a great quantity of thermal medium is disadvantageously supplied to the other line or air conditioners which is not subject to a large heat load and accordingly does not require a large quantity of thermal medium.